South Korea will buy European bunker-busting missiles as the United States refused to sell the same kind of weapons to the country, the state procurement agency said on Wednesday.

At a meeting presided over by Defence Minister Kim Kwan-Jin, the Defence Acquisition Program Administration (DAPA) approved a plan to purchase air-to-ground missiles with a 500-kilometre (312.5 mile) range from the German-Swedish joint venture Taurus System.

The number of missiles and proposed budget have not been confirmed yet, it said. But Yonhap news agency said South Korea planned to buy about 170 Taurus bunker busters worth more than $300 million in total.

Launched from a relatively safe distance from the enemy, the GPS-guided cruise missiles can hit strategic targets with precision, DAPA said in a press statement.

"The long-range air-to-ground missiles will add to our strategic assets, bolster deterrence against war and drastically enhance survivability of the aircraft and pilots as well", DAPA said.

Currently, the only long-range missiles in the Air Force's inventory are 40-odd SLAM-ER missiles with a range of 278 kilometres, Yonhap said.

DAPA had planned to choose between Taurus and Joint Air-to-Surface Standoff Missiles (JASSM) by US giant Lockheed Martin.

But the Pentagon has not approved the sales of the 370-km range missile, classified as a strategic weapon, to South Korea.

"In the face of mounting threats from North Korea, we need to acquire them at an earliest possible date. However, the acquisition of JASSM has become infeasible due to the US government's decision", DAPA said.

On Tuesday, South Korea formally opened bidding on a $7.3 billion deal to provide 60 advanced fighter planes, with three aviation giants vying for what is the Asian nation's largest defence contract to date.

US companies Boeing, Lockheed Martin and the European aerospace consortium EADS are in the running and all have prefaced their bids with various sweeteners to try and edge out their rivals.